As a related-art technique of a distortion compensation apparatus of a power amplifier, for example, a proposal has been made of an amplifier with a distortion compensation function, which has an amplifier, a means for obtaining a difference signal between an input signal of the amplifier and an output of the amplifier, a means for generating a compensation coefficient for compensating a distortion characteristic component of the amplifier from the difference signal using an adaptive algorithm, a means for outputting the generated compensation coefficient in accordance with the input signal, and a means for multiplying the input signal by the compensation coefficient output in accordance with the input signal and inputting the result into the amplifier.
In another example of a related-art technique, a distortion compensation apparatus compensating distortion characteristic of an amplifier includes an adjacent-channel leakage power extraction means, a distortion-compensation-coefficient calculation means, and a distortion-compensation-coefficient application means. The adjacent-channel leakage power extraction means is configured to extract at least an adjacent-channel leakage power of a main channel signal to be distortion-compensated from an output signal of the amplifier. The distortion-compensation-coefficient calculation means configured to convert an amplitude value and a phase value of a distortion compensation coefficient into genotypes, respectively and to obtain the distortion compensation coefficient based on a genetic algorithm using the adjacent-channel leakage power value or an adjacent-channel leakage power rate value obtained from the adjacent-channel leakage power value as an evaluation function. And the distortion-compensation-coefficient application means is configured to apply the distortion compensation coefficient calculated by the distortion-compensation-coefficient calculation means to the input signal of the amplifier.
Also, as another example of a related-art technique of a distortion compensation apparatus of a power amplifier, a proposal has been made of a distortion-compensation amplifier in which an A/D converter samples a feedback signal of an output of a power amplifier, an equalizer of a distortion detection section detects an equalization error of a quadrature demodulated signal using an input signal of a predistorter as a reference symbol, an absolute-value averaging section outputs an average value of the equalization error in time to a control section as a distortion value, and the control section controls the predistorter adaptively based on the distortion value to perform distortion compensation.
Also, in another example of a related-art technique, a distortion-coefficient detection section 32 independently detects an amplitude third-order distortion and a phase third-order distortion constituting a coefficient related to at least third-order intermodulation distortion among coefficients related to a third-order intermodulation distortion, coefficients related to a fifth-order intermodulation distortion, and coefficients related to a seventh-order intermodulation distortion out of distortion components arising in a power amplifier from an output signal of the power amplifier and an input signal. And a distortion-compensation generation circuit generates a distortion compensation signal based on at least the detected amplitude third-order distortion and phase third-order distortion, and at least either the generated distortion-compensation signal or the input signal is passed through a variable delay filter, and then added by a multiplier.
Also, in another example of a related-art technique, a distortion-generation path of a power-series type predistorter is provided with a frequency-characteristic compensator adjusting a frequency characteristic of a distortion component in series with an odd-numbered disorder generator, a distortion detector detects a distortion component from a transmission signal obtained by demodulating an output of a power amplifier, a distortion-component frequency characteristic divider divides the distortion component by a band-width window, distortion component power is obtained for each window, and based on the power, the frequency-characteristic compensator is controlled to adjust a portion corresponding to the above-described window in the frequency characteristic of the distortion component.
Also, in another example of a related-art technique, a transmission apparatus includes a learning-signal generation section generating a learning signal, a power detection section detecting signal power of a transmission signal, and a control section obtaining appearance probability of a signal power of a transmission signal based on the signal power detected by the power detection section and adding the learning signal in accordance with the appearance probability during signal transmission.